bmillikanphd / laz-perf

Alternative LAZ implementation for C++ and JavaScript

What is this?

LAZperf is an alternative LAZ implementation. It supports compilation to WASM via Emscripten so that LAZ data can be decoded in a browser.

Building LAZperf for Windows/UNIX

Previous versions of LAZperf were header-only C++ libraries, so you could simply include the project header files in your project. Primarily due to licensing issues, this is no longer the case and LAZperf needs to be built as a library that links with your code. LAZperf uses CMake as a build system, though it's probably simple to port to another build system as there are few source files and no dependencies. Assuming you have Git, CMake, make and C++11 compiler installed, here is the process on the Unix command line. The process is similar on Windows.

git clone https://github.com/hobu/laz-perf.git
cd laz-perf
mkdir build
cd build
cmake ..
make

This should build the library liblazperf.so (or similar). You can install this library along with the supporting header files as follows:

make install

Using LAZperf on Windows/UNIX

Although the LAZperf library is focused on decoding the LAZ data itself, there is support for reading a complete LAS or LAZ file. If you have LAZ-compressed data, you can decompress by creating a decompressor for the right point type and providing a callback that will provide data from the LAZ source as requested by the decompressor. For example, to read point format 0 data, you might do the following:

using namespace lazperf;

void cb(unsigned char *buf, int len)
{
    static unsigned char my_laz_data[] = {...};
    static int idx = 0;

    std::copy(buf, buf + len, my_laz_data + idx);
    idx += len;
}

point_decompressor_0 decompressor(cb);

char pointbuf[100];
for (int i = 0; i < num_points; ++i)
{
    decompressor(pointbuf);
    // Do something with the point data in 'pointbuf'
}

Compression follows a similar pattern -- see the accompanying examples and tests.

You can also use LAZperf to read LAZ data from an entire LAZ or LAS file:

using namespace lazperf;

reader::named_file f(filename);

char pointbuf[100];
for (size_t i = 0; i < f.header().point_count; ++i)
    f.readPoint(pointbuf);

A memory file interface exists If your LAS/LAZ data is internal rather than in a file:

using namespace lazperf;

reader::mem_file f(buf, bufsize);

char pointbuf[100];
for (size_t i = 0; i < f.header().point_count; ++i)
    f.readPoint(pointbuf);

Using LAZperf in JavaScript/TypeScript

Install

LAZperf is available as a UMD module compatible with both NodeJS and browsers, and includes TypeScript definitions.

npm install laz-perf

Usage

import { createLazPerf } from 'laz-perf'

const LazPerf = await createLazPerf()

// File reader API.
const laszip = new LazPerf.LASZip()
laszip.open(filePointer, fileByteLength)
for (let i = 0; i < pointCount; ++i) {
    laszip.getPoint(dataPointer)
    // Do something with point data.
}

// Chunk decoder API.
const decoder = new LazPerf.ChunkDecoder()
decoder.open(pointDataRecordFormat, pointDataRecordLength, chunkPointer)
for (let i = 0; i < pointCount; ++i) {
    decoder.getPoint(dataPointer)
    // Do something with point data.
}

See unit tests in js/src/test for further details and how to interact with the Emscripten heap to work with the data.